STUDY OF RELAXATION TRANSITIONS IN SOME AROMATIC POLYESTERS

Методом спинового зонда проведено систематическое изучение основных релаксационных переходов жесткоцепных стеклообразных полимеров в широком интервале температур с применением спиновых зондов разного размера на примере полисульфона. В главной области релаксации ароматических полиэфиров с помощью метода спинового зонда обнаружены два перегиба. Два перегиба, обнаруженные на температурной зависимости времени корреляции вращения, являются следствием размораживания сегментальной подвижности в областях с различной упаковкой сегментов. Показано, что высокотемпературный перегиб соответствует размораживанию сегментальной подвижности кооперативного типа (а -переходу), а перегиб при более низкой температуре р -размораживанию сегментальной подвижности локального типа (а'-процессу). Для объяснения природы данного перехода была использована теоретическая модель полимера, где предполагается, что в аморфных полимерах возможны разные уровни надмолекулярной организации, т.е. существование более упорядоченных и более плотно упакованных областей, которые чередуются с более «рыхлыми» и менее упорядоченными областями. Исследовано влияние различных факторов на положение а’-перехода на температурной шкале. Выбор объема зонда на основе строго обоснованной модели его движения позволил выявить взаимосвязь между вращательным движением зонда и движением отдельных сегментов аморфного полимера ниже температуры стеклования. The spin probe method was used to systematically study the main relaxation transitions of rigid-chain glassy polymers in a wide temperature range using spin probes of different sizes using polysulfone as an example. In the main relaxation region of aromatic polyesters, two inflections were found using the spin probe method. The two inflections found in the temperature dependence of the rotation correlation time are the result of unfreezing of segmental mobility in regions with different packing of segments. It was shown that the high-temperature inflection corresponds to the defrosting of the cooperative-type segmental mobility (a -transition), and the inflection at a lower temperature corresponds to the / -defrosting of the segmental mobility of the local type (the a' -process). To explain the nature of this transition, a theoretical model of the polymer was used, where it is assumed that different levels of supramolecular organization are possible in amorphous polymers, i.e. the existence of more ordered and more densely packed regions, which alternate with looser and less ordered regions. The influence of various factors on the position of the a' -transition on the temperature scale is investigated. The choice of the probe volume on the basis of a strictly substantiated model of its motion made it possible to reveal the relationship between the rotational motion of the probe and the motion of individual segments of the amorphous polymer below the glass transition temperature.

What is the primary mover of water dynamics?

We present evidence that the microscopic origin of both the excess wing and the main relaxation process of pure water is the same.

OLED degradation described by using a time-dependent local relaxation model

The main mechanisms responsible for the luminance degradation in OLEDs driven under constant current has not yet been identified. In this paper we propose a new approach to describe the intrinsic mechanisms involved in the OLED aging. We will first show that a stretched exponential decay can be used to fit almost all the luminance vs time curves obtained under different driving conditions. In this way we are able to prove that they can all be described by employing a single free parameter model.By using as an approach based on local relaxation events, we will demonstrate that a single mechanism is responsible for the dominant aging process. Furthermore, we will demonstrate that the main relaxation event is the annihilation of one emissive center.We will then use our model to fit all the experimental data measured under different driving condition, and show that by carefully fitting the accelerated luminance lifetime-curves, we can extrapolate the low-luminance lifetime needed for real display applications, with a high degree of accuracy.

Dielectric relaxation of nonionic microemulsion: influence of the salinity

Study of dielectric properties of a quaternary microemulsion system composed of water, oil, a nonionic surfactant, and an alcohol, in the frequency range 100 kHz – 15 GHz is reported as a function of salt (NaCl) concentration. Depending on the salinity, the decomposition of the dielectric spectra shows the presence of two or three main relaxation domains. The lower relaxation frequency and the corresponding spectral amplitude increase as a function of salinity. The other observed relaxation mechanisms are shown to be dipolar in origin.PACS No.: 97.22Gn

The Room Temperature Dielectric Spectrum of 2,2-Dimethyl-1 -butanol

The dielectric spectrum of the title substance ('neohexanol') in its pure liquid state is reported for 293 K up to 71 GHz and, for a restricted frequency range, also for lower temperatures (down to 253 K). The room temperature spectrum resembles that of alicyclic alcohols, in particular cyclopentanol, with respect to spectral shape, main relaxation time and the relation of the latter to viscosity, which similarity may be connected with the fact that these alcohols are able to form 'plastic crystals'.

Dielectric Relaxation of 2-Amino-l-butanol

The dielectric relaxation spectrum of the title substance in mixtures with 1,4-dioxane or benzene (pure liquid to moderate mixture ratios) is measured between 5 MHz and 36 GHz at 20°C. The static permittivity is determined over the whole mixture range. The results are discussed in particular with respect to the possibility that different types of hydrogen bonded aggregations may contribute to the main relaxation

Proton and Fluorine Spin-Lattice Relaxation in Polycrystalline CoSiF6 · 6 H20

The spin-lattice relaxation times T1 (1H) and T1 (19F) in CoSiF6 · 6H20 have been measured at 30 MHz in the temperature range 150 K ≦ F ≦ 400 K Both T1 (1H) and T1 (19F) decrease sharply at the phase transition temperature of 246 K (cooling cycle). The main relaxation mechanism is assumed to be an Orbach process. From the T1 data an average splitting of the Co2+ ground state of about 400 cm-1 in both phases is obtained. The splitting is mainly caused by spin orbital coupling.